Previous studies demonstrated that vago-vagal reflex plays a crucial role in the mediation of postprandial pancreatic enzyme secretion. During the last funding period, we demonstrated that luminal stimuli induced the release of 5-HT from mucosal EC cells, which in turn activated 5-HT3 receptors on mucosal vagal afferent terminals to stimulate vagal primary sensory neurons; in this manner, 5-HT acts as a paracrine substance to stimulate pancreatic secretion via a vagal cholinergic pathway. The current proposal is designed to characterize the neurochemical transmission in the vagal afferent pathway of nodose ganglia neurons to NTS neurons, and the vagal efferent pathway of DMN preganglionic neurons to intrapancreatic neurons, which mediate pancreatic secretion stimulated by luminal 5-HT-dependent factors. We hypothesize that glutamate and substance P are the major neurotransmitters responsible for transmitting afferent information from vagal primary afferent neurons to the NTS. The integration of activities excited by multiple neurotransmitters at the DMN plays a critical role in modulating the vagal efferent signaling to the pancreas: NPY and SP stimulate, while somatostatin inhibits DMN neurons. Specific groups of DMN neurons may innervate specific intrapancreatic neurons, which contain different neurotransmitters. To test this hypothesis we plan to perform pancreatic retrograde tracing, c-Fos, and neurotransmitters immunocytochemistry to characterize the vagal primary afferent pathway, as well as the NTS and DMN neurons, which are activated by luminal stimulation. Electrophysiological recording followed by labeling of nodose ganglia and NTS neurons will further confirm the neurotransmitters and receptors involved in the transmission of afferent inputs to the NTS. We will record the firing of the vagal pancreatic nerves and identify the chemical codings of the intrapancreatic ganglia neurons activated by DMN stimulation. Finally, we will examine the roles of various neurotransmitters in the DMN in the mediation of pancreatic secretion stimulated by luminal 5HT-dependent factors using a conscious rat model.